Giraffa camelopardalis AMNH

Rios, M, Danowitz, M & Solounias, N, 2016, First comprehensive morphological analysis on the metapodials of Giraffidae, Palaeontologia Electronica 410 (10453), pp. 1-39 : 31-35

Giraffa camelopardalis AMNH 70016

460 54 11.74 Kostopoulos, 2009

475 52.1 10.97 Kostopoulos, 2009

450 54.6 12.13 Kostopoulos, 2009

430 Kostopoulos, 2009

447 49.5 11.07 Kostopoulos, 2009

56.4 Kostopoulos, 2009

47 Kostopoulos, 2009

52 Kostopoulos, 2009

420 45 10.71

462 53 11.47 Geraads, 1994

420 25 5.95

445 32.8 7.37 Kostopoulos, 2009

32.5 Kostopoulos, 2009

30 Kostopoulos, 2009

377 30 7.96 Geraads, 1994

714 50 7.00

52.97

49.36

49.4

48.33

690 Geraads et al., 2005

709 48 6.77

680 46 6.76 Geraads et al., 2005

670 55.5 8.28 Kostopoulos et al., 1996

680 51.8 7.62 Kostopoulos et al., 1996

658 49 7.45 Geraads et al., 2005

695 52.5 7.55 Geraads et al., 2005

56 Geraads et al., 2005

692 50 7.23

620 Mecquenem, 1924

675 52 7.70 Geraads et al., 2005

702 48.43 6.90

680 49 7.21

742 52 7.01

658 45 6.84

638 39.24 6.15

625 39.32 6.29

765 50.86 6.65

626 40.02 6.39

764 49.52 6.48

685 45.43 6.63

686 44.75 6.52

TABLE 4 (continued).

( Figures 20 , 23 ). Therefore, additional features are needed to separate and define the giraffids. In the taxa with short metapodials, Canthumeryx exhibits a shallow trough, whereas the trough of Sivatherium and the okapi is intermediate in depth. The depth of the trough separates the elongate-metapodial giraffids as well; the central trough of Bohlinia is notably deep, whereas it is shallow in the giraffe. The central trough is a useful character that provides better separation between taxa than absolute metapodial length.

Heinz (1963) described proximal metatarsal morphologies that can be used to distinguish between cervids and bovids. Bovids exhibit a facet on the proximal plantar surface termed the diarthrodial facet, whereas cervids possess a bony protrusion in this position termed the posterior tuberosity. The term diarthrodial refers to a distinct facet adjacent to the main facet. Janis and Scott (1987) utilized the presence of the posterior tuberosity to unite cervids and palaeomerycids. The pygmaios of giraffids described in the present study presents as relatively distinct from the proximal shaft and is positioned more centrally at the proximal plantar metatarsal surface. The morphology, size, and presence of the pygmaios are variable among the different giraffid species ( Figure 16 ). While it is possible that the pygmaios is homologous to the posterior tuberosity described in cervids, we believe this is a separate structure that should not be used to unite the two groups. The giraffid pygmaios may also be homologous to the metatarsal sesamoid bone, which is variable among artiodactyls.

The presence and morphology of the giraffid pygmaios is another character that can be used to separate the metatarsals. Within the sivatheres, this structure is absent in Helladotherium , Sivatherium , and Birgerbohlinia , and is reduced and protrudes less proximally than the other giraffids in Bramatherium . In certain giraffids, the pygmaios is notably distinct from the medial and lateral epicondyles by deep medial and lateral grooves, as is seen in Deccenatherium, Samotherium , and Bohlinia . When present, it is rounded in all giraffids, with the exception of the primitive Canthumeryx , where it is pointed, and in the okapi and Bohlinia , where the proximal end is flattened. In the palaeotragines Samotherium and Palaeotragus , as well as in Birgerbohlinia , the pygmaios is oriented medially, and Canthumeryx is unique in that this structure is directed centrally. In the giraffe, the pygmaios is absent; however, there is a large depression with lipped edges in its position. When combined with the other metatarsal features, the presence, orientation, and distinctness of the pygmaios are useful features to separate giraffid genera.

The giraffid metatarsal is characterized by medial and lateral epicondyles, which are each separated into dorsal and plantar heads. The heads of the medial and lateral epicondyles are distinct in all giraffids; however, the grooves creating the separation are narrower and fainter in the giraffe. Another character uniting Giraffidae is the orientation of the medial and lateral epicondyles; the dorsal heads of all giraffid medial and lateral epicondyles flare outward, and the plantar heads are relatively straight. In Samotherium and Palaeotragus , the outward flaring of the dorsal head is more pronounced on the medial epicondyle. The Canthumeryx metatarsal represents the most extreme outward flare. While there are subtle differences between the individual species, the distinctness and general orientation of the heads of the medial and lateral epicondyles are features that are shared in the metatarsals of all giraffids.

The metatarsal proximal morphology ( Figure 18 ) can also be used to separate between giraffids. While in Helladotherium duvernoyi, Bramatherium megacephalum , Birgerbohlinia schaubi , and Okapia johnstoni the os cuneiforme intermediolaterale and os cuneiforme mediale facets are separated, in Decennatherium pachecoi , Samotherium major , and Sivatherium giganteum both facets are in contact in a small point, and in Giraffa camelopardalis they can be contacting or slightly separated.

Morphological features of the giraffid metapodials are key characters that can be used in future genus and species identifications. Figures 4 , 7 , 16- 17 demonstrate that no two genera share the same combination of metapodial characters; each genus can be characterized by a unique combination of metapodial morphological features. Unlike dimensional features that show general metapodial patterns ( Solounias, 2007), detailed morphological features allow for genus level identifications. Using these descriptions and simplified character tables, a giraffid metapodial specimen can be identified as either a genus included in this study, or as a new taxon. Our morphological characters can also be applied to bovids, cervids, and camelids to enrich the systematic investigations of known and unknown species.

Giraffid metapodials range largely in both length and robustness ( Tables 1-6) providing with the possibility of establishing certain categories that can serve as a tool for future phylogenetic inferences. In the past, other authors have used these features of the appendicular skeleton to describe and separate between the different giraffid species ( Hamilton, 1978; Morales and Soria, 1981; Solounias, 2007).

The oldest giraffid in our sample, Canthumeryx sirtensis , would fall in the category of short and very slender ( Figure 22 ; Tables 1-6). Most late Miocene giraffids have medium metapodials in both length and robustness, except Palaeotragus rouenii that is on the slender side and Bohlinia attica , that has long and very slender metapodials ( Figures 19 , 22 ; Tables 1-6). The geographically younger Sivatherium giganteum falls into its own robustness category as the only extremely robust giraffid ( Figures 19 , 22 ; Tables 2, 5). The extant Okapia johnstoni is short and slender and Giraffa camelopardalis shares the same long and very slender metapodials as Bohlinia attica .

Metapodial robustness (RI) is a useful feature, giving us information about how the animal is built in terms of its gracility ( Morales and Soria, 1981). All the giraffids in our analysis, with the exception of Palaeotragus rouenii , had a higher RI in the metacarpals when compared to the metatarsals ( Tables 2, 5). This supports that giraffids distribute more body weight on the forelimb instead of the hindlimb, contrary to the typical condition seen in artiodactyls ( Alcalde, 2012). The highest metacarpal RI of our analysis, Sivatherium giganteum , could be correlated with the presence of massive ossicones ( Falconer and Cautley, 1836; Basu et al., 2016), which would place a higher weight on the anterior part of the body. The same occurs with the robust Bramatherium megacephalum ( Lewis, 1939) , which also bears huge ossicones and Birgerbohlinia schaubi which bears 50 cm long posterior ossicones ( Montoya and Morales, 1991).

In addition to the robustness, we find the minimum diameter versus length provides valuable information on the limb proportions and possibly level of sexual dimorphism and variability of the different taxa. The metapodial proportions are highly consistent in Okapia johnstoni ; in this taxon, the individual specimens all plot within a tight length and width range ( Figures 21 , 24 ). The metapodials of Sivatherium giganteum and Helladotherium duvernoyi, however, are more variable in minimum diameter, and those of the modern giraffe are variable in both length and width. The variability in

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Figures

FIGURE 4. Three selected metacarpal characteristics. This simplified table can be used to facilitate specimen identifications and differentiate between different giraffid taxa.

FIGURE 7. Three additional metacarpal characteristics. This simplified table can be used to facilitate specimen identifications and differentiate between different giraffid taxa.

FIGURE 16. Three selected metatarsal characteristics. This simplified table can be used to facilitate specimen identifications and differentiate between different giraffid taxa.

FIGURE 18. Metatarsal proximal morphology. 1, Helladotherium duvernoyi, late Miocene, Pikermi, M 1138; 2, Bramatherium megacephalum, late Miocene-Pliocene, Siwaliks, AMNH 19688; 3, Decennatherium pachecoi, late Miocene, Los Valles de Fuentidueña, MNCN 42764; 4, Birgerbohlinia schaubi, late Miocene, Piera, IPS 5090. Abbreviations: NC, os naviculocuboideum facet; CIL, os cuneiforme intermediolaterale facet; CM, os cuneiforme mediale facet. Images not to scale.

FIGURE 19. Box-and-whiskers plot with the metacarpal RI of the Giraffidae analyzed.

FIGURE 20. Dispersion plot with the absolute metacarpal length of the Giraffidae analyzed. TABLE 3. Descriptive parameters of the metacarpal length of the Giraffidae (Max., maximum; Min., minimum; SD, standard deviation; Ntotal, total sample size).

FIGURE 21. Dispersion plot showing the total length of the metacarpals versus the midshaft minimum transverse diameter of the Giraffidae analyzed.

FIGURE 22. Box-and-whiskers plot with the metatarsal RI of the Giraffidae analyzed.

FIGURE 23. Dispersion plot with the absolute metatarsal length of the Giraffidae analyzed.

FIGURE 24. Dispersion plot showing the total length of the metatarsals versus the midshaft minimum transverse diameter of the Giraffidae analyzed.